In the field of computer network systems, and in particular industrial computer network systems, there are various scenarios where the network parameters within a network device are required to be changed, for example due to another device being added or removed from the network, or when a redundancy switchover between master devices is required to be performed. FIG. 1 schematically illustrates a simplified block diagram of an industrial computer network system 100 comprising two master devices 110, 120. Slave devices 130 within the computer network system 100 of FIG. 1 are arranged in a multi-drop configuration, such as may be implemented within, say, a PROFIBUS (Process Field Bus) computer network. Other network configurations are equally possible, such as, say, a ring configuration as may be used within an Ethernet network, etc.
The first master device 110 is configured to actively control the slave devices 130 within the computer network system 100. The second master device 120 is configured in a redundant capacity, and as such is inactive in terms of controlling the slave devices 130. The redundant master device 120 may still participate in sending some frames on the network 100. For example, in a PROFIBUS network both master devices 110, 120 participate in token passing, but the second (redundant) master device 120 does not have slave devices 130 in its gap list to control. The first (active) master device 110 is connected to the redundant master device 120 via a protocol bus 140 (e.g. implemented by way of Industrial Ethernet, CAN, PROFIBUS etc.) and optionally via a dedicated link 150 for redundancy monitoring. This dedicated link 150 could be Ethernet, PCI or a proprietary interface.
In operation, both master devices 110, 120 are monitoring the bus 140 and their transmitted frame errors. A redundancy monitoring protocol, indicated generally at 160, is active and it decides when to take an active master device, such as the first master device 110 in FIG. 1, off the bus and when to switch an inactive master device, such as the redundant master device 120 in FIG. 1, to an active state. Such a change of state for the redundant master device 120 requires the network/configuration parameters and other data for the master device 120 to be changed.
Upon a master switchover (e.g. upon the active master device 110 being taken off the bus 140 and the redundant master device 120 being switched to an active state) the slave devices 130 should not be aware that they are being controlled by a different master device. However, state of the art systems require that the port of a network device be disabled or taken offline in order to synchronously and atomically switch from one master device to another and change the network/configuration parameters for the master device(s). Disabling or taking a master device offline in this manner results in a slow handover from one master device to another, increasing the risk of errors occurring within the computer network due to the master device being unavailable for a prolonged period of time. To ensure a handover that does not detrimentally impact system wide behaviour when disabling or taking a device offline, this requires complex software that must run to completion, must not be interrupted, must run within a known timeframe and must be guaranteed a certain proportion of CPU cycle bandwidth.